Stochastic forcing of sediment routing and storage in channel networks

Abstract

The stochastic field of sediment supply to the channel network of a drainage basin depends on the large‐scale interactions among climatically driven processes such as forest fire and rainstorms, topography, channel network topology, and basin scale. During infrequent periods of intense erosion, large volumes of colluvium are concentrated in parts of a channel network, particularly near tributary junctions. The rivers carry bed material and wash load downstream from these storage sites at different rates. The bed material travels slowly, creating transient patterns of sediment transport, sediment storage, and channel morphology along the channel network. As the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion, interference at tributary junctions, and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion, which converts bed material to wash load. We investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215‐km2 drainage basin within the Oregon Coast Range over a simulated 3000‐year period with a climate typical of the late Holocene. We used field measurements and a simulation model to illustrate interactions between the major controls on large‐scale processes functioning over long periods of time in complex drainage basins.